What is Anaerobic Digestion?

Anaerobic Digestion (often abbreviated to A.D.) is a process that uses harmless natural bacteria to digest biomass (such as food waste, crops or slurry) in the absence of oxygen and convert soluble organic compounds present in the biomass into a stream of biogas and a sludgy fiborous material. The process is performed in sealed tanks so as to capture the biogas and the fiborous material. 

Anaerobic Digestion - The Process

Biogas produced from an AD process is a mixture of methane and carbon dioxide with a typical ratio of 60:40. These are then separated to generate pure methane, also known as Biomethane.

 

Biomethane can be used to directly substitute fossil-derived natural gas commonly used in households for heating, cooking and hot water production.

 

Once the biogas is produced from the AD process it is sent to a gas-upgrading unit designed to separate the carbon dioxide and biomethane. The carbon dioxide is released back into the air, which will be used to grow the following year’s crops. The plant forms a closed loop carbon cycle as the biogenic carbon dioxide released from this process will have been collected from the previous year’s crop production.

 

The valuable biomethane is then piped through a special National Grid metering unit used to monitor the energy output of the plant. At this stage it is injected into the adjoining gas pipe owned by the National Grid. Once the biomethane enters the local gas grid network it is distributed and to local homes and businesses as a displacement of fossil-derived natural gas.